The present application is related to U.S. patent application Ser. No. 10/994,754, filed on Nov. 22, 2004, now U.S. Pat. No. 7,124,689, issued Oct. 24, 2006. The disclosure of the above-mentioned applications is incorporated by reference herein in its entirety.
1. Field of the Invention
This invention relates generally to fuzes for explosive devices and, more particularly, to determining an environmental condition related to when an explosive device may be safely armed.
2. Description of Related Art
Explosive projectiles must be capable of being handled safely under considerable stress and environmental conditions. In addition, explosive projectiles must be capable of detonating at the proper time. Depending on the application, this proper time may be before impact at a specific point during flight, during impact, or at some time delay after impact. As used herein the terms “warhead,” “explosive device,” and “explosive projectile” are generally used to refer to a variety of projectile type explosives, such as, for example, artillery shells, rockets, bombs, and other weapon warheads. In addition, these explosive projectiles may be launched from a variety of platforms, such as, for example, fixed wing aircraft, rotary wing aircraft (e.g., helicopters), ground vehicles, and stationary ground locations. To determine the proper detonation time, these explosive projectiles frequently employ fuzes.
A fuze subsystem activates the explosive projectile for detonation in the vicinity of the target. In addition, the fuze maintains the explosive projectile in a safe condition during logistical and operational phases prior to launch and during the first phase of the launch until the explosive projectile has reached a safe distance from the point of launch. Consequently, major functions that a fuze performs are: keeping the weapon safe, arming the weapon when it is a safe distance from the point of launch, detecting the target, and initiating detonation of the warhead at some definable point after target detection.
The first two functions are conventionally referred to as Safing and Arming (S&A). Safing and Arming devices isolate a detonator from the warhead booster charge until the explosive projectile has been launched and a safe distance from the launch vehicle is achieved. At that point, the S&A device removes a barrier from, or moves the detonator in line with, the warhead, which effectively arms the detonator so it can initiate detonation at the appropriate time.
Some S&A devices function by measuring elapsed time from launch, while others determine distance traveled from the launch point by sensing acceleration experienced by the weapon. Still other devices sense air speed or projectile rotation. For maximum safety and reliability of a fuze, the sensed forces or events must be unique to the explosive projectile when deployed and launched, not during ground handling or pre-launch operations. Most fuzes must determine two independent physical parameters before determining that a launch has occurred and a safe separation distance has been reached.
Detecting spin of the projectile is an often-used physical parameter. However, explosive projectiles that are not shot through a rifled barrel tend to exhibit very low angular accelerations. These smaller angular accelerations and spin rates are more difficult to detect. Conventional spin sensors such as accelerometers and spin switches set to detect these low angular accelerations may be spoofed by accelerations related to platform maneuvers prior to launch.
Other conventional spin sensors detect the Earth's magnetic field and sense changes in position and orientation of the spinning projectile relative to the Earth's magnetic field. These devices may be quite complex and may be susceptible to electro-magnetic noise or electro-static noise.
There is a need for a straightforward device and robust method to sense low angular accelerations of explosive projectiles in flight while being insensitive to cross-axis accelerations from projectile launch. In addition, there is a need to discriminate between platform maneuver accelerations and spin accelerations related to projectile flight after separation from the projectile launch point.
An embodiment of the present invention comprises a spin sensor, including a fuze housing, a sense weight, and a rotating induction device. The rotating induction device comprises a first element affixed to the fuze housing and a second element affixed to the sense weight. The second element is mechanically coupled to the first element such that it may rotate relative to the first element. In addition, the second element is inductively coupled to the first element such that a relative rotation between the first element and the second element generates a spin signal on an electrical connection to the rotating induction device.
Another embodiment of the present invention comprises an explosive projectile including an encasement, an explosive material disposed within the encasement and configured for detonation, and a spin sensor disposed within the encasement. The spin sensor comprises a fuze housing, a sense weight, and a rotating induction device. The rotating induction device comprises a first element affixed to the fuze housing and a second element affixed to the sense weight. The second element is mechanically coupled to the first element such that it may rotate relative to the first element. In addition, the second element is inductively coupled to the first element such that a relative rotation between the first element and the second element generates a spin signal on an electrical connection to the rotating induction device.
Another embodiment of the present invention comprises a method of sensing fuze spin. The method comprises providing a sense weight rotationally coupled to a fuze housing, rotating the fuze housing, and detecting a relative rotation between the sense weight and the fuze housing. The method further comprises converting the detected relative rotation into a spin signal, which is sampled to develop an actual spin profile of the fuze housing. The developed actual spin profile may then be compared to an acceptable spin profile.
Yet another embodiment, in accordance with the present invention comprises a method of sensing fuze spin including inductively coupling a first element affixed to a fuze housing and a second element affixed to a sense weight. The inductive coupling generates a spin signal correlated to a relative rotation of the first element relative to the second element. The spin signal is sampled to develop an actual spin profile of the fuze housing. The developed actual spin profile may then be compared to an acceptable spin profile.
In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:
In the following description, circuits and functions may be shown in block diagram form in order not to obscure the present invention in unnecessary detail. Conversely, specific circuit implementations shown and described are exemplary only and should not be construed as the only way to implement the present invention unless specified otherwise herein. Additionally, block definitions and partitioning of logic between various blocks is exemplary of a specific implementation. It will be readily apparent to one of ordinary skill in the art that the present invention may be practiced by numerous other partitioning solutions. For the most part, details concerning timing considerations and the like have been omitted where such details are not necessary to obtain a complete understanding of the present invention and are within the abilities of persons of ordinary skill in the relevant art.
In this description, some drawings may illustrate signals as a single signal for clarity of presentation and description. It will be understood by a person of ordinary skill in the art that the signal may represent a bus of signals, wherein the bus may have a variety of bit widths and the present invention may be implemented on any number of data signals including a single data signal.
In describing the present invention, the systems and elements surrounding the invention are first described to better understand the function of the invention as it may be implemented within these systems and elements.
As explained earlier, part of the S&A function is to prevent premature detonation. The exemplary fuze embodiment may incorporate multiple independent environments to determine that the explosive projectile 100 may be safely armed. One environment incorporated in the exemplary embodiment of the fuze 200 is spin sensing. Spin sensing may be used to determine that the explosive projectile 100 has been launched and is following a normal trajectory wherein the spin may be caused by a rifled barrel or the aerodynamic characteristics of the explosive projectile 100.
The rotating induction device 310 may be a device such as an alternator or an electric motor and may also be referred to herein as an alternator 310 or as an electric motor 310. Generally, an exemplary alternator 310 includes a first element affixed to the fuze housing 220 and a second element affixed to the sense weight 390. The first element and the second element are rotationally coupled and inductively coupled. In various embodiments, the first element may be a stator of the alternator 310 or a rotor of the alternator 310. Similarly, the second element may be a rotor of the alternator 310 or a stator of the alternator 310.
As shown in
In the exemplary embodiment of the spin sensor 300 shown in
In another embodiment of the spin sensor 300′ shown in
In another embodiment, rather than using a conventional AC alternator 310 or AC motor, a direct current (DC) alternator 310′ or DC motor may be used, as shown in
Conventional alternators and electric motors exhibit an attribute known as magnetic detent. This is an angular resistance to relative rotation between the rotor 320 and stator 330. The rotor 320 and stator 330 may not rotate relative to one another until a relative angular acceleration is large enough to overcome the force of the magnetic detent. In the present invention, magnetic detent may be used to resist relative rotation of the rotor 320 and stator 330 for small angular accelerations or vibrations that may be encountered during platform maneuvers or transportation of the explosive projectile 100. Furthermore, because the device is not sensitive to these cross-axis accelerations, precise alignment of the sensor to the longitudinal axis of the explosive projectile 100 is not needed.
This exemplary embodiment employs redundant, low power microcontrollers as the main analyzer 370 and the safety analyzer 370′. In the exemplary embodiment, the safety analyzer 370′ is a different part from a different vendor than the main analyzer 370. The dual-analyzer configuration using differing parts enables a cross-checking architecture, which may eliminate both single point and common mode failures. However, other analyzer configurations are contemplated within the scope of the present invention. For example, a single analyzer may be used or more than two analyzers may be used to enable additional redundancy and safeguards against failures.
It may be advantageous to condition the spin signal 340 generated from the alternator 310 (
In operation of the exemplary embodiment of the spin sensor 300 shown in
By way of one, nonlimiting example, an acceptable spin profile may be defined as at least four transitions from the spin sensor 300, with each transition occurring at an increasing rate. The system may be configured such that the main analyzer 370 and the safety analyzer 370′ wait for a signal from the initiation sensor 380 indicating a valid launch event. After a valid launch event, the analyzers 370 and 370′ may sample the spin signal 340 to develop the actual spin profile. If the actual spin profile conforms to the acceptable spin profile, the analyzers 370 and 370′ may signal that a valid spin environment has been achieved. If the actual spin profile does not conform to the acceptable spin profile within an expected time window, a valid spin environment may have not been achieved and the fuze 200 may be shut down.
In addition, if multiple analyzers are used, a valid spin environment may require all analyzers to reach a same conclusion on a comparison of the actual spin profile to the acceptable spin profile. Of course, a person of ordinary skill in the art will recognize that many other spin profiles are contemplated within the scope of the present invention.
Although this invention has been described with reference to particular embodiments, the invention is not limited to these described embodiments. Rather, the invention is limited only by the appended claims, which include within their scope all equivalent devices or methods that operate according to the principles of the invention as described.
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